1. Field of the Invention
The present invention relates to a lens system of a two-focus switching type; and, in particular, to a two-focus switchable lens which is suitable for a compact, low-cost still camera and the like.
2. Description of the Prior Art
There have recently been strong demands for taking pictures according to object positions while switching between telephoto and wide-angle modes even in compact, low-cost still cameras.
As techniques of such a kind, those disclosed in Japanese Unexamined Patent Publication Nos. 7-281092 and 9-021946 have been known. The former is of a type comprising two lenses of negative and positive ones, in which the positive lens is moved so as to change the focal length; whereas the latter is of a type in which a lens on the wide-angle side and a lens on the telephoto side are switched therebetween.
In the former, however, not only a mechanism for moving the lens is necessary, but both the total lens length and the outside diameter of the negative lens become greater, whereby it may be problematic from the viewpoint of achieving compactness.
In the latter, on the other hand, each of the wide-angle and telephoto lenses is constituted by two elements of positive and negative lenses, so that four lenses in total are necessary, thereby contradicting the demands for achieving lower cost and compactness.
Also, when a wide-angle-side lens and a telephoto-side lens are used in a switchable fashion, it is necessary to employ a configuration in which the difference between their respective aperture stop positions is reduced in order to yield a smaller shutter diameter in response to the demand for compactness. However, it has been difficult to increase the power ratio of telephoto/wide angle in a simple configuration while satisfying such a requirement.